Chemical and biological separations are routinely performed in various industrial and academic settings to determine the presence and/or quantity of individual species in complex sample mixtures. There exist various techniques for performing such separations.
One particularly useful analytical process is chromatography combined with mass spectroscopy, which encompasses a number of methods that are used for separating ions or molecules for analysis. Liquid chromatography (“LC”) is a physical method of separation wherein a liquid ‘mobile phase’ carries a sample containing a mixture of compounds or ions for analysis (analytes) through a separation medium or ‘stationary phase.’ Fluid from the LC device, which comprises both the analytes and the mobile phase, is provided the analytes to an ion source of a mass spectrometer (MS) for spectroscopic analysis.
Often an electro-spray system is used in the interface between the LC device and a mass spectrometer. In electro-spray systems, a voltage is applied to the mobile phase to charge the fluid, and a gas may be provided to assist in nebulizing the fluid. As the fluid comprising the mobile phase and analytes exits a tube or channel annular gas flow around the tube or channel exit forms drops from the fluid. The fluid drops have a charge and, as the mobile phase begins to evaporate, the charge can be transferred to the analytes.
Unfortunately, and among other shortcomings, known drying methods are comparatively low-energy processes and therefore require the drops to travel a significant distance to desolvate. Moreover, repulsion of ions due to known space charge repulsion causes rarefaction. Decreased sample density translates to a comparatively small fraction of the sample ions entering the MS and, hence, reaching a detector in the MS. As such, the efficiency of the MS is reduced.
What is needed, therefore, is a method and apparatus for providing analytes from an LC column to a mass analyzer that overcomes at least the drawbacks of known devices and methods described above.